In a wireless communications system, a base station allocates a radio resource to a terminal, to implement data transmission. The radio resource allocation process is also referred to as a scheduling process. Scheduling may include uplink scheduling and downlink scheduling. Uplink scheduling is used to allocate an uplink resource to the terminal, so that the terminal sends data on the uplink resource. Downlink scheduling is used to allocate a downlink resource to the terminal, so that the base station uses the downlink resource to send data to the terminal.
Uplink scheduling may be triggered by a scheduling request (SR) or a buffer status report (BSR). That is, when a terminal needs to send uplink data, the terminal may trigger, by reporting the SR or the BSR, a base station to allocate an uplink resource to the terminal. For example, referring to FIG. 1, FIG. 1 is a schematic diagram of an existing uplink scheduling process. As shown in FIG. 1, in the uplink scheduling process, when a terminal needs to send uplink data, the terminal sends an SR to a base station to inform the base station that the terminal needs to send the uplink data; and after receiving the SR, the base station delivers an uplink grant (UL Grant) to the terminal. The uplink grant indicates a resource allocated to the terminal. After receiving the uplink grant, the terminal sends a BSR by using the resource indicated by the uplink grant, to inform the base station of a volume of the uplink data to be sent by the terminal, so that the base station allocates more uplink resources to the terminal based on the BSR, and delivers an uplink grant. In this way, the terminal can continue transmitting uplink data by using a resource indicated by the uplink grant. In addition, the uplink data may also be sent while the BSR is being sent.
When a serving cell of the terminal changes (for example, handover occurs), or the terminal re-accesses the serving cell because of some reasons, the terminal also triggers uplink scheduling by sending an SR or a BSR. For example, when being handed over from a source cell to a target cell, the terminal reports an SR in the target cell, or sends a BSR when the handover is completed, to trigger uplink scheduling.
It can be learned that, in the prior art, the terminal can trigger uplink scheduling only after handover on the terminal is completed. A relatively long time is required for cell handover. As a result, an uplink data transmission latency of the terminal is relatively long, thereby affecting user experience. In particular, for a service with a relatively high latency requirement (such as a voice service), such latency is even unacceptable.